This application claims priority from R.O.C. Patent Application No. 090124497, filed Oct. 4, 2001, the entire disclosure of which is incorporated herein by reference.
The present invention relates generally to semiconductor manufacturing and, more particularly, to an improved method for forming dual oxide layers at the bottom of a trench of a substrate.
To achieve an increase in integration and smaller ICs (integrated circuits), the DMOS (Double Diffused Metal Oxide Semiconductor) is commonly used in semiconductor manufacturing. The manufacturing of DMOS requires the formation of an oxide layer, called bottom oxide layer, at the bottom of a trench to reduce the charge produced from turning on the DMOS and to decrease the leakage current.
The conventional procedure for forming dual oxide layers at the bottom of a trench is described as follows. Referring to FIG. 1a, a semiconductive substrate 100 having a trench 110 and a mask layer 120 is provided.
Referring to FIG. 1b, an oxide layer 130 is formed on the sidewall and the bottom of trench 110. The oxide layer 130 is a self-aligned contact oxide layer formed by thermal oxidation.
Referring to FIG. 1c, a HMDS (hexamethyl disilazane) coating treatment 140 is performed. The HMDS coating treatment 140 is used as a priming treatment before coating photoresist.
Referring to FIG. 1d, a photoresist layer 150 is deposited on the mask layer 120, and the trench 110 is filled up with the photoresist layer 150.
Referring to FIG. 1e, a curing treatment 160 is performed to cure the photoresist layer 150.
Referring to FIG. 1f, the photoresist layer 150 is partially etched to leave a remaining photoresist layer 150xe2x80x2, wherein the thickness of the remaining photoresist layer 150xe2x80x2 is lower than the depth of trench 110.
Referring to FIG. 1g, the mask layer 120 and part of the oxide layer 130 are removed by BOE (buffered oxide etchant) treatment, wherein the bottom of trench 110 is left with a remaining oxide layer 130xe2x80x2 and a remaining photoresist layer 150xe2x80x2.
Referring to FIG. 1h, the remaining photoresist layer 150xe2x80x2 is removed.
Referring to FIG. 1i, another conformal oxide layer 170 is formed on the substrate 100, the sidewall of the trench 110 and the remaining oxide layer 130xe2x80x2. The region 180 includes the remaining oxide layer 130xe2x80x2 on the bottom of trench 110 and the portion of the conformal oxide layer 170 on the bottom of trench 110. In specific embodiments, the height of the dual oxide layer structure 180 on the bottom of the trench 110 is about 0.2 xcexcm to about 0.3 xcexcm.
The disadvantage of the method of prior art is that when the depth of the trench 110 is very deep in FIG. 1e, especially deeper than 1.0 xcexcm, vaporization of the solvent of the photoresist 150 in the trench 110 is very difficult. This causes the adhesion between the remaining photoresist layer 150xe2x80x2 and the oxide layer 130 to be weak. Then, when performing the BOE treatment in FIG. 1f to FIG. 1g, the BOE etchant will damage the interface 200 between the remaining photoresist layer 150xe2x80x2 and the oxide layer 130. The oxide structure at the bottom of trench 110 is also damaged, as illustrated in the FIG. 2.
Embodiments of the present invention are directed to an improved method for forming dual oxide layers at the bottom of a trench of a substrate. Instead of curing the photoresist layer prior to partial etching, the photoresist curing treatment is performed after partial photoresist ashing or etching. This allows the easy vaporization of the solvent of the remaining photoresist in the trench. By performing a curing treatment to completely, or substantially completely, vaporize out the solvent of the remaining photoresist layer in the trench, the method produces a strong interface between the remaining photoresist layer and the first bottom oxide layer. As a result, the damage to the interface between the remaining photoresist layer and the first bottom oxide layer by the BOE etchant is minimized, and improved dual oxide layers can be produced by forming the second bottom oxide layer over the first bottom oxide layer.
In accordance with an aspect of the present invention, a method of forming dual oxide layers at the bottom of a trench comprises providing a substrate having a trench which includes a bottom and a sidewall. A first oxide layer is formed on the sidewall and the bottom of the trench of the substrate. A photoresist layer is formed on the substrate, filling the trench of the substrate. The method further comprises partially etching back the photoresist layer to leave a remaining photoresist layer in the trench. The height of the remaining photoresist layer is lower than the depth of the trench. A curing treatment of the remaining photoresist layer is performed. A portion of the first oxide layer is removed to leave a remaining first oxide layer at the bottom of the trench. The remaining photoresist layer is removed. A second oxide layer is formed on the substrate covering at least the remaining first oxide layer.
In some embodiments, the trench is formed on the substrate by forming a mask oxide layer on the substrate; defining the mask oxide layer to form a patterned mask oxide layer and exposing a partial surface of the substrate to form a window; and using the patterned mask oxide layer as an etching mask to form the trench in the window. The patterned mask oxide layer is removed before forming the second oxide layer. The patterned mask oxide layer and the portion of the first oxide layer are removed to leave a remaining first oxide layer at the bottom of the trench by 10:1 BOE treatment. The mask oxide layer comprises a silicon oxide layer formed by thermal oxidation. The trench is formed in the window by dry etching.
In specific embodiments, an HMDS coating is formed on the surface of the first oxide layer before forming the photoresist layer. A heat treatment is performed on the HMDS coating. The heat treatment may be performed at about 70-150xc2x0 C. for about 40-100 seconds. The second oxide layer is a conformal oxide layer formed on the remaining first oxide layer, the sidewall of the trench, and the surface of the substrate. The method may further comprise performing a curing treatment on the photoresist layer after the photoresist layer is formed on the substrate filling the trench of the substrate. The first oxide layer comprises a self-aligned contact silicon oxide layer formed by thermal oxidation. The photoresist layer may be partially etched back by O2 plasma ashing. The curing treatment of the remaining photoresist layer may be performed at about 120-200xc2x0 C. for about 60-100 seconds. The second oxide layer comprises a silicon oxide layer formed by thermal oxidation. Performing the curing treatment of the remaining photoresist layer comprises at least substantially completely vaporizing out solvent of the remaining photoresist layer in the trench.
Another aspect of the present invention is directed to a method of forming dual oxide layers at the bottom of a trench wherein a substrate has a trench which includes a bottom and a sidewall, wherein the trench is formed on the substrate by forming a mask oxide layer on the substrate, defining the mask oxide layer to form a patterned mask oxide layer and exposing a partial surface of the substrate to form a window, and using the patterned mask oxide layer as an etching mask to form the trench in the window; wherein a first oxide layer is formed on the sidewall and the bottom of the trench of the substrate, wherein a photoresist layer fills the trench of the substrate; wherein the patterned mask oxide layer and a part of the first oxide layer are removed to leave a remaining first oxide layer at the bottom of the trench; wherein the photoresist layer is removed; wherein a second oxide layer is formed on the substrate covering at least the remaining first oxide layer. The improvement comprises, prior to removing the patterned mask oxide layer, a part of the first oxide layer, and the photoresist layer, partially etching back the photoresist layer to leave a remaining photoresist layer in the trench and performing a curing treatment of the remaining photoresist layer. The height of the remaining photoresist layer is lower than the depth of the trench.
In some embodiments, the photoresist layer is partially etched back by O2 plasma ashing. The curing treatment of the remaining photoresist layer is performed at about 120-200xc2x0 C. for about 60-100 seconds. The improvement further comprises performing a curing treatment on the photoresist layer after the photoresist layer is formed on the substrate filling the trench of the substrate.